Dual Fuel Tank Question

[Kirk T]

I have an '85 K10 with a mechanical fuel pump and it is equipped with dual tanks and the dash toggle switch. My question is should there be a voltage drop from the switch to the valve? I'm getting 12v at the switch and about 7 volts at the valve. The dash switch has 4 wires and I have checked wire continuity going back to the valve and everything seems good there. I am in the process of replacing the passenger side fuel tank (rusted out) and sending unit. I connected the new sending unit to chassis ground and the PNK/BLK wire that was on the original sending unit but when I move the float up and down, the fuel gauge does not react.

I'm a little bumfuddled and need some advice. I did read a post on the forum that said the dash switch had to be depressed for 2 seconds which I haven't been doing when testing.

Thank you

 

[dvdswan]

Silly question, when you checked the fuel level, did you have the key in the run position?

 

[Kirk T]

Yes I did.

 

[Kirk T]

I bought a new dash mounted switch and I'm confused about the way it works. If you press the switch and release it seems to go back to an open circuit. I put a test light on the pink wire to make sure I was getting 12 volts. I then put the test light on the DK GRN or LT GRN wire and they only activate if you hold the switch down. When you release the switch the light goes off. Is that right? I noticed on the box the switch came in it calls it a "momentary on rocker switch". I don't know if the switch is good or bad.

 

[Termite_Delight]

There are at least 2 different switches used between '73-'87. I make sure I press firmly when switching from 1 tank to the other. Make sure your tanks have good grounds.

 

[bucket]

The later style switch only works when you are pushing it, that's why it's a 'momentary' switch. It says "Depress Fully" or something along those lines on the original switch, to make sure you hold it long enough for the valve to fully switch over.

 

[Kirk T]

Okay, I get it now. It seems it is working fine now that I know a little better about what I'm doing. Thanks for the help.

 

[84K30]

I have a question regarding this same matter. Yesterday, I dropped my passenger tank, which had not been in use for an unknown period of time, due to a dry rotted filler hose. The fuel that did come out of the tank was similar to diarrhea water but the tank was spotless inside-no sludge or rust. I reconnected everything and decided to put only 5 gallons of fresh fuel in the tank in case I have to drop it again.

I have the depress fully switch which appears to need to be held for a period of time as it does not "lock" into a position when depressed. The truck stayed running but the fuel gauge pegged way past full when I held the button. It is my belief that the switch is currently in a position which reflects that the passenger side tank is working, however, I should know for sure in about 50 miles.

Since the OE switch is only $9 on Rock Auto, I went ahead and ordered one. Does anyone know which fuse, if any, is associated with the dual tank electrical circuit? Also, is there supposed to be a ground from the fuel tank sending unit to the body? If so, where does it connect on the sending unit mechanism?

Thanks,
Eric

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[HOTFOOT]

What ever that is in the bucket looks like it wants to kill something

 

[SquareRoot]

What ever that is in the bucket looks like it wants to kill something

My first thought. Maybe a club headed diarrhea butt fish?

 

[84K30]

Lurking in that 5 gallon bucket is the love child of New Mexico “moon dust and several gallons of the highest taxed gasoline in the nation.

Any idea on the fuse &/or sending unit ground locations?

 

[dvdswan]

IIRC, a pegged gas gauge is a sign of a short/open in the wire to the gauge from the tank. Actually, it would be from the tank to the switch, if the other tank fuel level works fine.

 

[84K30]

The other fuel tank level works fine. I’ll check the circuit from the pass tank sending unit to the selector switch after I change out the switch itself.

 

[84K30]

I believe I may have identified part of the issue... the ground wire which connects the fuel sending unit to the body is broken. Does anyone have a photo of where/how the wire connects to the sending unit?

 

[dusterdude]

The wire on my 85 appears to be crimped to the sending unit,I can shoot a pic tomorrow if you want.

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